The present invention is directed to a method for collecting light which utilizes a body functioning as a light trap, the body preferably is designed in plate shape and consists of a solid polymerized synthetic carrier containing fluorescent particles and is provided with at least one light exit window.
A light collector utilizing a body containing fluorescent particles or pigments is known in a various number of embodiments. For example, it may be used for collecting solar energy as disclosed in U.S. Pat. No. 4,110,123, which was based on German O.S. 26 20 115. Two other examples of such a solar collector used for capturing solar energy are disclosed by Paul M. Mauer et al, "Fluorescent Concentrator for Solar Energy Collection", Research Disclosure, January, 1975, No. 129, pages 20 and 21, and Goetzberger et al, "Solar Energy Conversion with Fluorescent Collectors", Applied Physics, Vol. 14, 1977, pages 123-139. Collectors, which utilize fluorescent particles, have also been used for optical transmission of messages as disclosed in copending U.S. Pat. application Ser. No. 932,569, which issued as U.S. Pat. No. 4,222,880 on Sept. 16, 1980 and is based on German application P 27 42 899, and for brightening the image of a passive display, as disclosed in both U.S. Pat. No. 4,142,781 which includes the disclosure of German O.S. 25 54 226 and in an article by W. Greubel et al, Elektronik, Vol. 6, 1977, pages 55 and 56. Collectors have also been used for increasing the sensitivity of a scintillator as disclosed by G. Keil, "Design Principles of Fluorescence Radiation Convertors", Nuclear Instruments and Methods, Vol. 87, 1970, page 111-123. Favorable processing conditions, carrier materials and possibilities for improving the light yields have already been described in copending U.S. application Ser. No. 062,816, which is based on German application P 28 33 914.2; U.S. Ser. No. 062,734 which is based on German application P 28 33 926.6 and U.S. Ser. No. 062,784 which was based on German application P 28 33 934.6.
When light strikes a fluorescent plate, then the component of the light lying in excitation spectrum of a fluorescent substance is absorbed by the fluorescent centers of the materials. The remaining light component will permeate the fluorescent plate undisturbed. The absorbed radiation is emitted by the fluorescent centers with a longer wave length and spatially undirected. Due to reflections at the plate interface a large part of the fluorescent light is conducted in the interior of the carrier plate until it emerges at specific coupling out regions with an increased intensity.
The efficiency achieved up until now with fluorescent plates still always lags behind the theoretical possible values. Mainly this is because the emission spectrum overlaps with the absorption spectrum and the fluorescent radiation of the plate therefore has a finite absorption length. What is particularly dissatisfying is that this "self-absorption" has a particularly unfavorable effect particularly on fluorescent bodies with a large collecting surface.
It has already been known for a long time that the emission band is displaced towards the lower frequencies with respect to the excitation band in some organic fluorescent substances when these particles are dissolved in a liquid with a strong orientation polarization. In the following it will be understood that pigments are unsolved or unsoluble dyes. Whereas particles are molecules solved in a liquid or a carrier. This displacement, which is known as a red shift occurs when the fluorescent molecule has different dipole moments in its basic or at rest state and its excitation state and when the environment which remains unchanged during the absorption process can re-orient during the existence of the excitation state as described in an article by E. Lippert, Zeitschrift fur Elektrochemie, Ber. Bunsengs. Phys. Chem. Vol. 61, No. 8, 1957, pages 962-975.
However, fluorescent bodies should consist insofar as possible of a solid carrier material. Solid carriers, which are organic synthetics, can be manufactured and processed with relatively low outlay which is an advantage, particularly in a mass production process.
The desired band separation in solid state solution also depends on the dielectric constant of the solid and the dipole differences between the rest state and the excited state also plays an important role. This is discussed in the above mentioned article from Applied Physics. Investigations of the suggested interrelationship which leads further and which investigation would teach one how to select the synthetics with the necessary polarization properties, are stil lacking. Above all, there is a lack of suggestion as to how one is to proceed so that the polar synthetics also fulfills the demands to be made of the fluorescent bodies. The fluorescent body, as well known, must be highly transparent and thermally as well as photochemically stable. In addition, the fluorescent bodies should be easy to bring into any desirable shape, must be hard and dimensionally stable in the final state, and should have a high fluorescent quantum yield.